1. FIELD OF THE INVENTION
The present invention relates to a sealing device for the rotor shaft of a fluid machine and, more particularly, to a sealing device provided with a solid packing extending circumferentially around the rotor shaft, the solid packing having a plurality of circumferentially spaced segments.
2. DESCRIPTION OF THE PRIOR ART
The sealing device conventionally used for the rotor shaft of a fluid machine has at least one solid packing extending circumferentially around the rotor shaft and disposed in a single stage or a plurality of stages in the axial direction of the rotor shaft. Each solid packing includes a plurality of circumferentially spaced segments with a suitable gap left between adjacent ones. These segments are accomodated and supported by an annular sealing box.
In operation of the fluid machine, the sealing box is distorted and angularly displaced by the action of the fluid at the high-pressure side of the sealing box. The distortion and the angular displacement of the sealing box in turn causes an angular displacement of the segments in the sealing box. At the same time, the segments themselves are angularly displaced due to the action of the fluid at the high pressure side. More specifically, each segment is made to incline such that the sliding surface thereof contacts the rotor shaft surface only at its edge adjacent to the high pressure side, while the edge of the same adjacent to the low pressure side is spaced away from the shaft surface. Consequently, the sliding surface in the inclined state defines, in cooperation with the rotor shaft surface, a wedge-shaped space in cross-section which opens at its low-pressure side end and closes at its high-pressure side end. Since the wedge-shaped space inconveniently allows the fluid to pass therethrough, the flow rate of the cooling fluid, which is intentionally made to pass through the gaps between the adjacent segments to cool them down, is increased impractically, so that the sealing performance of the sealing device is deteriorated considerably.
The deterioration of the sealing effect is more serious if each segment has a circumferential groove formed in the sliding surface and a fluid passage for introducing the fluid from the high pressure side into the groove for cooling the segment and for decreasing the surface pressure on the sliding surface, because the fluid will leak from the high pressure side through the fluid passage and the groove to the low pressure side, in addition to the above discussed leakage.
In addition, in the conventional sealing device of the kind described, the initial sliding contact between the rotor shaft surface and the segment is made only at the edge of the latter adjacent to the high pressure side. Thus, it takes a considerably long time until this edge is worn down to provide a contact area large enough to ensure the required sealing effect.